Field of the Invention
The present invention relates to an image processing apparatus for forming an image by using an electrophotographic system.
Description of the Related Art
Conventionally, a so-called image forming apparatus of the electrophotographic system is known, such as a laser beam printer and a copying machine, which forms an electrostatic latent image by irradiating the surface of a photoreceptor with a light beam in accordance with an exposure signal and develops the electrostatic latent image by causing toner to stick thereto. Then, as the exposure system, an LED system is known. In the LED system, a plurality of LED elements, which are light-emitting elements, is arranged in the lengthwise direction of a photoreceptor drum and a plurality of lenses to collect light that is output from the LED elements onto the photoreceptor drum is also arranged.
There is a system for modulating light emission intensity (exposure intensity) of the light-emitting element (hereinafter, intensity modulation system) for improving gradation and resolution of an output image in the image forming apparatus of the electrophotographic system such as the above (see Japanese Patent Laid-Open No. S61-277258 (1986)).
However, in the case where a latent image is formed by the intensity modulation system, the increase or decrease in the toner-stuck area on the photoreceptor is not linear with respect to the exposure intensity and there is a case where an image deterioration, such as the collapse of the linearity of density of the output image, may occur. In order to maintain linearity, it is necessary to find an optimum amount of correction for each tone level, and therefore, there is such a problem that time and effort are necessary and throughput is reduced.